The accurate reproduction of colored graphics has proven difficult using known color printing methods. This is primarily due to the fact that the methods employed to accomplish the reproductions are incapable of producing the high fidelity color and quality of the original image. One known method used to produce colored graphics employs the three process colors (cyan, magenta and yellow) to reproduce an image by first conducting a color analysis on the original and then making what are known as color separations and finally, printing the image. In the past, color separations were created by placing a red, green, and blue filter respectively over the lens of a camera and shooting a separation negative using panchromatic film (film sensitive to the visible portions of the spectrum). Use of these filters produced cyan, magenta and yellow separation negatives. Thus, these separations yielded a record of the amount and concentrations of the three process colors contained in the original. The color information contained in the negatives is then fed into a printer. The various tones and colors of the original image are approximated by printing patterns of various sized dots next to one another using each process color. When the final image is viewed, the dots tend to blend together to create what appears to be the colors corresponding to the colors found on the original image.
Historically, the dot patterns were determined using the halftone separation technique described above along with what is known as a halftone screen which was placed over the film during exposure to break up the image from the original copy into grids corresponding to the dot patterns to be printed. The dot patterns obtained from the combination of the halftone screen and the separation negatives, known as halftone dots, were then transferred to the printer which printed the patterns corresponding to each process color onto a receiving surface, thereby reproducing the original image.
More recently, the color analysis and halftone separations have been carried out in a single step using a color scanner and computer in combination with a printer. The color scanner evaluates the colored original point by point through color filters. The image is then converted from a visual to an electrical impulse that is fed into a computer. The computer then compiles this information and uses it to control a printer.
One type of printer particularly suited for printing the halftone dot patterns according to the information obtained from a scanned original is known as an ink jet printer. Typically, this type of printer uses a print head having three ink reservoirs each carrying a process colored (cyan magenta and yellow) ink. During a printing process, the print head traverses the image receiving surface and simultaneously prints the halftone dot patterns according to the color separations accomplished by the scanner and computer.
A problem often encountered with the images created by the above described process is that the patterns of dots are clearly visible. This causes the image to appear less sharp and in some cases even grainy. This is especially undesirable in situations where the images produced will be subject to close scrutiny. Accordingly, there is a need for a color image production technique which accurately reproduces an original using solid continuous colors. As used herein, the term continuous should be construed to mean that the appropriate portion of the receiving surface upon which the color is transferred is completely filled with color and contains no dots.
In addition to the foregoing, the previously described process is not capable of accurately reproducing many colors or shades of color. For instance the appearance of some subtle pastels cannot be duplicated using only the three process colors. Therefore, in some instances it may not be possible to acceptably reproduce a particular image.
A known method used to produce solid continuous colors, incorporates a thermal printer. Donor foils are utilized by the thermal printer, from which layers of color pigment are transferred to a receiving surface. The phrase "donor foil" is a term of art which denotes in one aspect, a foil or other thin material which carries a layer of pigment dispersed in a wax, resin, or wax-resin vehicle. The pigment is transferred from the foil to the receiving surface by the thermal printer through a combination of heat and pressure. Alternatively, in a second aspect, a donor foil can take the form of a dye diffusion foil or other thin material, wherein the foil or other thin material is impregnated with a transferable dye which when exposed to the heat and pressure produced by the thermal printer, diffuses out of the foil or other thin material and onto the print media. While this printing method consistently produces high quality continuous colors, it is limited by the available number of donor foil colors. The color of the dye or pigment carried by a donor foil is referred to by those skilled in the art as a "spot color." The finite number of available spot colors, has, until recently, caused this method of printing to be considered inappropriate for the accurate continuous color reproduction of images.
Based on the foregoing, there is a current need for a method of producing an expanded palette of solid continuous colors and shades of color producible from a limited number of donor foil colors. This method should be capable of producing the same high fidelity appearance on the print media, as is embodied in the original graphic. It is also important that the method employ a means of identification as well as the associated formula needed to reproduce each color and shade such that an operator is able to readily ascertain and print the desired color.
In accordance with the foregoing, it is the general object of the present invention to provide a greatly expanded palette of printable high fidelity continuous colors and shades, producible using a limited number of spot colors.
A further object of the present invention is to provide a means whereby these colors, and the formulas for their production are codified in an easily accessible fashion.